1. Field of the Invention
The present invention relates to a planetary gear train and a wind turbine generator using the mechanism, more particularly, to a structure of a thrust bearing of the planetary gear.
2. Description of the Related Art
The planetary gear train is one of mechanisms widely used as a step-up gear box and a reduction gear box. The planetary gear train has an advantage that a large reduction ratio can be obtained with a small number of gears and a large torque can be transferred. Such an advantage is preferable for a wind turbine generator, and the planetary gear train is widely used as the step-up gear box of the wind turbine generator.
One problem in applying a planetary gear train to a wind turbine generator is the lifetime of bearings of the planetary gears. When a planetary gear train is used as the gear box of the wind turbine generator, large loads are applied to the bearings of the planetary gears. Currently, rolling bearings are often used as the bearings of the planetary gears in the planetary gear train; however, the lifetime thereof will be reduced when large loads are applied to the rolling bearings. The increase in the load is a serious problem, especially in high-power wind turbine generators which have been recently developed.
The inventors have been considering using sliding bearings as bearings provided on the inner faces of the planetary gears as an approach for achieving a long lifetime and a reduced size of the bearings of the planetary gears. The sliding bearing can sustain the large load, since receiving the load with fluid oil film pressure. The use of sliding bearings, which can sustain a large load, may make it possible to realize a maintenance-free planetary gear train.
The use of a sliding bearing as a bearing of a planetary gear requires thrust bearings to be used in order to maintain a constant axial direction position of the planetary gear. A thrust bearing is typically composed of a circular sliding bearing member attached on the surface opposed to the planetary gear of the carrier. The circular sliding bearing member composing the thrust bearing may be referred to as “thrust collar” or “thrust washer”; hereinafter, the circular sliding bearing member is referred to as “thrust collar”. The thrust collar is made of steel (such as S45C and SS400), for example. Japanese Utility Model Application Publication No. JP-U 561-133146 (Patent literature 1) discloses a structure of a thrust bearing having a thrust collar, for example. In addition, Japanese Patent Application Publication JP-A 2002-242999 (Patent literature 2) discloses a structure for realizing the positional restriction in the axial direction of the planetary gear by a circular axial plate provided on the housing.
One issue of the structure of the thrust bearing of the planetary gear is a structure for fixing the thrust collar. An inadequate fixing structure may undesirably cause deterioration of the performance of thrust bearing or generation of a scratch on the sliding surface. For example, a structure for fixing the thrust collar by inserting bolts from the sliding surface requires holes formed on the sliding surface, and these holes undesirably reduce the area of the sliding surface, deteriorating the performance of the thrust bearing; in addition, the holes may cause a scratch formed on the sliding surface. Furthermore, a complicated structure for fixing the thrust collar is unpreferable in terms of productivity and production cost. Japanese Utility Model Application Publication No. JP-U S61-133146 discloses a structure in which openings are formed through the carrier in the direction parallel to the sliding surface and locking clicks provided for the thrust collar are inserted into the openings; however, such structure is undesirably complicated as the structure for fixing the thrust collar.